Solid phase microextraction-gas chromatographic-mass spectrometric determination of nitrous oxide evolution to measure denitrification in estuarine soils and sediments

A SPME-GC-MS method was developed to quantify nitrous oxide (N(2)O) to evaluate denitrification rates. There is a need for this sensitive and definitive N(2)O detection method to accurately measure the soil and sediment ability to convert anthropogenic mineral nitrogen loads to N(2) through denitrification hence decreasing estuarine waterway pollution loading. This method is applied to measure denitrification, which is a major pathway for inorganic nitrogen removal, by incorporating the acetylene (C(2)H(2)) block method on anaerobic assays. Currently, denitrification is largely measured using GCs fitted with TCD or ECD detectors. With a mean R(2) value of 0.996, the calibration curve spanned over three orders of magnitude (4.1-2030 nM) with a limit of detection (LOD) of 4.1 nM N(2)O (18 ppb) and a limit of quantification (LOQ) of 16 nM N(2)O (72 ppb). This detection method was valid with less than 15% relative standard deviation (RSD) and error for middle and high quality control (QC) points and less than 20% for low QC points on three experimental days. Measuring N(2)O using SPME-GC-MS technology allows for confidence in identification, high sensitivity, reproducibility, and short run times.     

Use of a novel nitrification inhibitor to reduce nitrous oxide emission from (15)N-labelled dairy slurry injected into soil

Recent recommendations for environmentally sound use of liquid animal manure often include injection of slurry into soil. Two of the most important undesired side effects, ammonia (NH(3)) volatilisation and odour emissions, are usually significantly reduced by slurry injection. On the other hand, because of the higher amount of nitrogen (N) remaining in soil, the risk of nitrate (NO(3)(-)) leaching and nitrous oxide (N(2)O) emissions is increased. Thus, the reduction of local effects caused by NH(3) deposition, e.g. N enrichment and soil acidification, may be at the cost of large-scale effects such as ozone depletion and global warming as a result of emitted N(2)O. In this context, nitrification inhibitors can contribute significantly to a reduction in NO(3)(-) leaching and N(2)O production. A field experiment was carried out at IGER, North Wyke, which aimed to evaluate the effect of the new nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP/ENTEC). For this experiment, (15)N enriched dairy slurry was used and the isotopic label in soil N as well as in N(2)O were studied. After slurry injection into the grassland soil in August 2000, the major emissions of N(2)O occurred during the first ten days. As expected, high N(2)O emission rates and (15)N content of the emissions were concentrated on the slurry injection slots, showing a steep decrease towards the untreated centre-point between slurry injection slots. The nitrification inhibitor DMPP proved to be very efficient in reducing N(2)O emissions. At a rate of 2 kg DMPP ha(-1), the total amount of N(2)O emitted was reduced by 32%, when compared with slurry injection without DMPP. The isotopic label of the emitted N(2)O showed that during the 22-day experimental period, emissions from the slurry N pool were strongly reduced by DMPP from 0.93 kg N(2)O-N ha(-1) (-DMPP) to 0.50 kg N(2)O-N ha(-1) (+DMPP), while only a minor effect on emissions from the soil N pool was observed (0.69 to 0.60 kg N(2)O-N ha(-1); -DMPP, +DMPP, respectively).     

氮肥管理对夏玉米土壤CH4和N2O排放的影响

通过设置四个不同的氮肥管理措施, 即氮肥施用量300 kg N/ha (N300)和250 kg N/ha (N250)、改进的施肥模式(Optimized)以及施用缓释肥(SRU), 研究华北平原夏玉米生长季土壤与大气之间CH₄和N₂O的交换通量及相应措施的减排潜力. 结果表明, 在2008年整个夏玉米生长季, 土壤都是大气CH₄的净吸收库和N₂O的排放源. 夏玉米生长季土壤氧化吸收的CH₄总量从大到小依次为Optimized > N250 > SRU > N300, 对应的吸收总量依次为624.16、590.07、487.89以及316.02 g CH₄-C/ha, 各处理间氧化吸收的CH₄总量无显著差异. 与N300和N250这两个处理相比, 依据夏玉米对氮肥的需肥规律以及玉米根层土壤速效氮的供给能力而确定氮肥施用量, 同时再平衡施用磷肥和钾肥的改进施肥模式能够显著降低夏玉米生长季N₂O的排放. 施用聚乙烯包膜的尿素也能够显著降低夏玉米季N₂O的排放. 夏玉米生长季土壤排放的N₂O总量从大到小依次为N300 > N250 > Optimized > SRU, 对应的排放总量依次为3462.18、2340.07、1680.00以及911.91 g N2O-N/ha, 相应的N₂O排放系数分别为1.15%、0.94%、0.91%以及0.30%.     

Tunnelling electron transfer from bulk electron centers of magnesium oxide to adsorbed molecules of nitrous oxide

Tunneling electron transfer from bulk F⁺-centers of MgO to molecules of N₂O adsorbed on MgO surface has been detected and studied.

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F⁺- N₂O, .

     

Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositions

Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using in situ field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was 15N- and 18O-depleted compared with N2O in local ambient air. The mean delta values of the soil-emitted N2O were delta15N = -13.5 +/- 3.2 per thousand and delta18O = 26.2 +/- 1.4 per thousand for the penguin colony, delta15N = -11.5 +/- 5.1 per thousand and delta18O = 26.4 +/- 3.5 per thousand for the skua colony and delta15N = -18.9 +/- 0.7 per thousand and delta18O = 28.8 +/- 1.3 per thousand for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93 microg N2O--N kg(-1)). Under N2 conditions, much more N2O was formed (9.74 microg N2O--N kg(-1)), and the mean delta15N and delta18O values of N2O were -19.1 +/- 8.0 per thousand and 21.3 +/- 4.3 per thousand, respectively, from penguin colony soils, and -17.0 +/- 4.2 per thousand and 20.6 +/- 3.5 per thousand, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N2O source from Antarctic sea animal colonies.     

Valorisation to biogas of macroalgal waste streams: a circular approach to bioproducts and bioenergy in Ireland

Seaweeds (macroalgae) have been recently attracting more and more interest as a third generation feedstock for bioenergy and biofuels. However, several barriers impede the deployment of competitive seaweed-based energy. The high cost associated to seaweed farming and harvesting, as well as their seasonal availability and biochemical composition currently make macroalgae exploitation too expensive for energy production only. Recent studies have indicated a possible solution to aforementioned challenges may lay in seaweed integrated biorefinery, in which a bioenergy and/or biofuel production step ends an extractions cascade of high-value bioproducts. This results in the double benefit of producing renewable energy while adopting a zero waste approach, as fostered by recent EU societal challenges within the context of the Circular Economy development. This study investigates the biogas potential of residues from six indigenous Irish seaweed species while discussing related issues experienced during fermentation. It was found that Laminaria and Fucus spp. are the most promising seaweed species for biogas production following biorefinery extractions producing 187–195 mL CH₄ gVS^?1 and about 100 mL CH₄ gVS^?1 , respectively, exhibiting overall actual yields close to raw un-extracted seaweed.     

Radiation removal of lead from aqueous solutions—effects of various sorbents and nitrous oxide

The influence of selected adsorbents (active carbon, bentonite and zeolite) on the radiation removal of lead from its aqueous solution using electron beam radiation was investigated. Both positive and negative effects on radiation reduction of Pb²⁺ ions depending on the dose applied were observed in presence of these solid modifiers. Besides deaeration with nitrogen, the efficiency of the process under study may be substantially increased by saturation of solution with nitrous oxide.     

Reaction of nitrous oxide with methane to synthesis gas: A thermodynamic and catalytic study

The aim of the present study is to explore the coherence of thermodynamic equilibrium predictions with the actual catalytic reaction of CH4 with N_2O,particularly at higher CH4 conversions.For this purpose,key process variables,such as temperature(300℃-550℃) and a molar feed ratio(N_2O/CH4 = 1,3,and 5),were altered to establish the conditions for maximized H_2 yield.The experimental study was conducted over the Co-ZSM-5 catalyst in a fixed bed tubular reactor and then compared with the thermodynamic equilibrium compositions,where the equilibrium composition was calculated via total Gibbs free energy minimization method.The results suggest that molar feed ratio plays an important role in the overall reaction products distribution.Generally for N_2O conversions,and irrespective of N_2O/CH_4 feed ratio,the thermodynamic predictions coincide with experimental data obtained at approximately 475℃-550℃,indicating that the reactions are kinetically limited at lower range of temperatures.For example,theoretical calculations show that the H2 yield is zero in presence of excess N2O(N_2O/CH_4 = 5).However over a Co-ZSM-5 catalyst,and with a same molar feed ratio(N_2O/CH_4) of 5,the H_2 yield is initially 10%at 425℃,while above450℃ it drops to zero.Furthermore,H_2 yield steadily increases with temperature and with the level of CH4 conversion for reactions limited by N_2O concentration in a reactant feed.The maximum attainable(from thermodynamic calculations and at a feed ratio of N_2O/CH4=3) H_2 yield at 550℃ is 38%,whereas at same temperature and over Co-ZSM-5,the experimentally observed yield is about 19%.Carbon deposition on Co-ZSM-5 at lower temperatures and CH4 conversion(less than 50%) was also observed.At higher temperatures and levels of CH_4 conversion(above 90%),the deposited carbon is suggested to react with N_2O to form CO_2.     

Microwave extraction of heavy metals from wet rhizosphere soils and its application to evaluation of bioavailability

Single microwave extraction of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb by the extractants CaCl(2), EDTA, CH(3)COOH and HCl has been established. The experimental conditions were optimized. A microwave power of 60% and an extraction time of 25 min were adopted. Comparison of microwave extraction and conventional extraction methods revealed that results obtained by microwave techniques were generally in a good agreement with those obtained by use of extraction methods; use of the former resulted in substantial time saving and a better precision, however. Microwave extraction was used to evaluate the bioavailability of heavy metals in soils. Single correlation analysis was performed to establish the relationship between the concentrations of the extractable heavy metals in wet rhizosphere soils and their concentrations in wheat ( Troticum aestivum L.) grown on the soils under greenhouse conditions. The correlation coefficients between the extractable metals in soils and their concentrations in wheat roots were found to be 0.5398-0.7819, 0.6425-0.8073, 0.5568-0.8276, 0.5851-0.6087 for the extractants CaCl(2), EDTA, CH(3)COOH, and HCl, respectively.     

Physical properties and application development of recycled products from waste plastics

The degradation of the physical properties of polypropylene (PP) used for automotive outer trims for several years is unexpectedly small. It, therefore, can be fully anticipated that PP so used can be recycled for the same purpose or for other applications.     

Photocatalytic deoxygenation of N–O bonds with rhenium complexes: from the reduction of nitrous oxide to pyridine N-oxides

The accumulation of nitrogen oxides in the environment calls for new pathways to interconvert the various oxidation states of nitrogen, and especially their reduction. However, the large spectrum of reduction potentials covered by nitrogen oxides makes it difficult to find general systems capable of efficiently reducing various N-oxides. Here, photocatalysis unlocks high energy species able both to circumvent the inherent low reactivity of the greenhouse gas and oxidant N₂O (E⁰(N₂O/N₂) = +1.77 V vs. SHE), and to reduce pyridine N-oxides (E_1/2(pyridine N-oxide/pyridine) = −1.04 V vs. SHE). The rhenium complex [Re(4,4′-tBu-bpy)(CO)₃Cl] proved to be efficient in performing both reactions under ambient conditions, enabling the deoxygenation of N₂O as well as synthetically relevant and functionalized pyridine N-oxides.

A rhenium-based photocatalyst enables the deoxygenation of several compounds containing N–O bonds, such as N₂O and pyridine N-oxides.     

Synthesis of multi-functional epoxides derived from limonene oxide and its application to the network polymers

Bio-based multi-functional epoxides (1) such as bis-, tri-, and tetra-epoxides were synthesized by ene-thiol reactions between limonene oxide and polyhydric thiols. A cross-linking reaction of 1 with branched polyethyleneimine (BPEI) afforded the corresponding network polymers 2 with relatively high thermal resistance in high yields.     

Observation of infrared free-induction decay and optical nutation signals from nitrous oxide using a current modulated quantum cascade laser

Free induction decay (FID), optical nutation, and rapid passage induced signals in nitrous oxide, under both optically thin and optically thick conditions, have been observed using a rapid current pulse modulation, or chirp, applied to the slow current ramp of a quantum cascade (QC) laser. The variation in optical depth was achieved by increasing the pressure of nitrous oxide in a long path length multipass absorption cell. This allows the variation of optical depth to be achieved over a range of low gas pressures. Since, even at the highest gas pressure used in the cell, the chirp rate of the QC laser is faster than the collisional reorientation time of the molecules, there is minimal collisional damping, allowing a large macroscopic polarization of the molecular dipoles to develop. This is referred to as rapid passage induced polarization. The resultant FID signals are enhanced due to the constructive interference between the field within the gas generated by the slow ramp of the laser (pump), and that of the fast chirp of the laser (probe) signal generated by pulse modulation of the continuously operating QC laser. The FID signals obtained at large optical depth have not been observed previously in the mid-infrared regions, and unusual oscillatory signals have been observed at the highest gas pressures used.